The Magnox Stations

Calder Hall had been designed to produce plutonium with electricity generation a secondary consideration. Indeed, the two reactors of Calder Hall A were to be followed by a further two at Calder Hall B, then four more at Chapelcross in Scotland. These were capable of generating 60 MW of power each, and Chapelcross was formally opened in May 1959. Since these stations were required for military purposes, responsibility for them stayed with the AEA, whereas later power stations would be owned and operated by the CEGB. 

Investigation and clearing out of the channel was not at all straightforward, since all operations had to be done by remote control. To make things more awkward, the chaimel in question was not directly below the opening in the pressure vessel biological shield. Specially made tools had to be used to grind out the debris in the channel and remove it. Eventually it proved necessary to bore out the entire channel to increase its diameter by 0.5 inches. 

Whilst the exact cause was never established, two small pieces of graphite sleeve, of a type different from that in the channel, had probably been lodged in the channel entry. This would have restricted the gas flow through the channel, and the fuel element would have become hot enough to melt the magnesium cladding. Even when the channel had been cleared, decontaminating the reactor took a very considerable time, so that it was not until June 1969, just over two years later, that the reactor was restored to full power. 

The magnox stations were intended as an improved version of the PIPPA or Calder Hall reactors, but whereas Calder Hall was optimised to produce plutonium. 

Needless to say, even before work had begun on what would become Calder Hall, a PIPPA Mark II was being considered. Some obvious improvements could be made, such as increasing the heat output and improving the efficiency for steam production. The Mark II study was for a power station to produce 100 MW (E), and among the changes were  

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Again, as much use as possible is made of simulation techniques, but at present this is very limited for those coming from the Magnox stations. This is because they... 

The British experience with circulators and associated shaft seals has been reported to be satisfactory for the magnox stations (48), including parallel operation of circulators. Demonstration testing of the helium circulators for the Peach Bottom power station has also been successful, including satisfactory performance of the shaft seals, which... 

Problems encountered in the operation of the magnox stations included (a) early difficulties with the complex refuelling equipment, (b) vibration of components due to gas glow, and (c) corrosion of gas circuit steel components in the carbon dioxide atmosphere. The last of these has proved the most serious, since it has led to the imposition of a reduction in power output in order to maintain the gas outlet temperature at a value where the corrosion rate is low enough to assure an economic life for the reactor. The problem is confined to small components, such as nuts and bolts made from low-silicon mild steel, and there is no danger to the more massive components of the pressure circuit. 

V. On-load refueling with a machine of simpler design than that used in the magnox stations maximum fuel burn-up of 18,000 MW d/tonne. 

The third part of the organisation was the industrial and production work, centred at Risley in Cheshire, again with various outposts for different functions.The factory at Springfields near Preston in Lancashire produced uranium hexafluoride for the diffusion plant, and manufactured uranium metal from the ore for use in fuel elements. It would also manufacture the fuel elements for all the commercial power stations, as well as the magnox stations built in Italy and Japan. The diffusion plant itself was sited at Capenhurst in Cheshire. There was also a Reactor Materials Laboratory at Culcheth, Warrington, in Cheshire. 

There is often confusion between the plutonium from the civil reactors — that is the magnox stations operated by the CEGB — and the plutonium from the Calder Hall and Chapelcross reactors. Calder Hall and Chapelcross were always operated by the AEA, and their initial purpose had been to produce plutonium for military purposes. This meant that the fuel had to be changed at relatively frequent intervals, so as to ensure relatively little °Pu content. The fuel in the civil reactors would have had a far greater burn up time and would have little miUtary value. There were times when demand for military plutonium was low and the output of the AEA reactors would then be optimised for electricity production rather than plutoninm production. 

Wylfa was the last of the magnox stations to be built, and its construction — or, at the least, the tender for its construction — would cause considerable controversy, highlighting the contradictions in government policy. Indeed, it could be said that it highlighted the lack of any government policy. 

By 1963, the consortia had been reduced to three in number. One of these was the UPC. The consortia in general were not happy with the government s policy, feeling that it was too short term. They had suffered as the nuclear programme had first been expanded in 1957, and then cut back later. A further problem was that Wylfa would be the last of the magnox stations, and it was not clear what was going to happen after Wylfa. Thus they faced a distinctly uncertain future. 

Rather than being closed, some of the magnox stations were to soldier on for nearly another half a century under reduced power. 

The route to the magnox reactors used for the first power programme is easy to trace the air-cooled Windscale piles lead to the idea of closed-circuit gas-cooling, which in turn lead to the PIPPA design and Calder Hall. Calder Hall can be considered as a prototype for the magnox stations, and the commercial versions took the design to its limit. 

The first power programme was for the total of 5,000 MW of electricity to be generated by nuclear means. The magnox stations had been taken as far as was feasible. The question then was what should follow the magnox stations. There was a vast range of possibilities, some of which would be more practicable than others. 

A timetable was laid out which recognised that the existing nuclear power programme of the magnox stations would be completed by the end of 1968. Building for the new programme would have to start in mid-1965 for a station to be commissioned in 1969, and so invitations to tender for the contracts would have to be sent out early in 1964. If the station was to be of a new type, the CEGB would require about nine months to prepare specifications for tender thus work would have to start by mid-1963. A decision was therefore required within about 12 months as to the type of reactor to be built. ... 

The paper went on to make comparisons between the last and most efficient of the magnox stations, Wylfa, and the AGR design ... 

Dungeness B was the first station to be ordered as a result of the 1964 White Paper it was to be the first of the AGRs which would replace the magnox stations, and it was to be the source of great controversy. 

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